1. Field of the Invention
The present invention relates to a method of producing a contact pin, particularly its mounting portion, by which the contact pin can be press-fitted in a plated-through hole of a printed circuit board.
2. Description of the Prior Art
Numerous designs of mounting portions of such contact pins are known. The German application DE-OS No. 29 30 560, for example, describes a contact pin having two resilient legs. Its mounting portion is produced by splitting its shaft which is of square cross section and simultaneously expanding it with the aid of two wedges. During the expanding step, the split shank halves are pressed against shell-shaped abutments, and are thus provided with a rounded surface. A contact pin having a mounting portion which ensures better distribution of forces is disclosed in U.S. Pat. No. 3,545,080. In one embodiment of that pin three resilient members are formed by stamping several slots and cutouts into a blank of flat stock. The bridges thus obtained are bent to form the spring members and the metal sheet is subsequently rolled up to form a hollow contact pin having three spring members disposed at 120.degree. from each other. The shank of such a contact pin, however, has a circular cross-sectional area and is thus unsuitable for wire-wraping.
EP-A-O No. 105 044 discloses a contact pin of rectangular cross section whose mounting portion is cut out from a central part which is wider than the shank. With the aid of two longitudinal cuts, three resilient legs are formed, the central one of which is bent in one direction in the plane of the cut, while the other two are bent in the opposite direction.
The rear ends of the two outer resilient legs overlap the corresponding end of the central leg. Thus, when the contact pin is inserted into a hole, the center leg acts like a wedge which is clamped by the two outer legs taking up a V-shaped position. This arrangement of three legs, however, limits their resilient properties.
A method of producing a contact pin of the type to be made according to the present invention is described in the German application DE-OS No. 25 45 505. As in EP-A-O No. 105 044, three resilient legs are stamped, of which two outer ones are twisted away from each other in an additional step so that all three surfaces designed to make contact with the hole wall are equidistant from each other. In the twisting step, the rear ends of the legs are brought to a position in which they are only a small distance apart from each other, whereby the deflection of the resilient legs is closely limited.